Here is the full list of all 41 Dark Souls (GFWL) achievements worth 1,000 gamerscore. It takes around 60-80 hours to unlock all of the achievements.
Defeat Crossbreed Priscilla, the Lifehunter.
Reach "The Dark Lord" ending.
Acquire all sorceries.
Acquire best weapon through crystal reinforcement.
Acquire best weapon through chaos reinforcement.
Acquire best weapon through magic reinforcement.
Reach "To Link the Fire" ending.
Acquire best weapon through fire reinforcement.
Acquire best weapon through enchanted reinforcement.
Acquire best weapon through standard reinforcement.
Acquire best weapon through occult reinforcement.
Acquire best weapon through divine reinforcement.
Defeat the Soul Lord Bed of Chaos.
Defeat Dark Sun Gwyndolin, the Darkmoon God.
Defeat Seath the Scaleless, inheritors of souls.
Acquire best weapon through lightning reinforcement.
Discover Path of the Dragon covenant.
Defeat the Soul Lord Gravelord Nito.
Discover Darkwraith covenant.
Defeat the Four Kings, inheritors of souls.
Acquire the Art of Abysswalking.
Discover Princess's Guard covenant.
Acquire the Lordvessel.
Discover Blade of the Darkmoon covenant.
Arrive in Anor Londo.
Discover Forest Hunter covenant.
Discover Way of White covenant.
Discover Gravelord Servant covenant.
Discover Chaos Servant covenant.
Ring Bell of Awakening in Quelaag's domain.
Arrive in Lordran.
Acquire the Rite of Kindling.
Discover Warrior of Sunlight covenant.
Ring Bell of Awakening at Undead Church.
Acquire Estus Flask.
Light bonfire flame.
All achievements completed. Congratulations!
Acquire all rare weapons.
Acquire all pyromancies.
Acquire all miracles.
Acquire best weapon through raw reinforcement.